After adding a bunch of points to a Polygon, can I reuse it or must I create a new one?

You can call reset() to remove the existing set of points from a Polygon. With that said, according to the javadoc: All internally-cached data relating to the old vertices are discarded. Note that since the coordinate arrays from before the reset are reused, creating a new empty Polygon might be more memory efficient than resetting the current one if the number of vertices in the new polygon data is significantly smaller than the number of vertices in the data from before the reset.